We study and compare four algorithms for adaptive retrieval of slowly
time-varying multiple cisoids in noise: the adaptive notch filter, the
multiple frequency tracker, the adaptive estimation scheme, and the h
yperstable adaptive line enhancer, The local behavior of the algorithm
s in a neighborhood of their equilibrium state [assuming high signal-t
o-noise ratio (SNR) and large data sample] for a two cisoid signal is
treated in a similar way to the linear filter approximation technique
used for a single-cisoid case. Validity of the results is confirmed by
computer simulations.